Time evolution of damage under variable ranges of load transfer

We study the time evolution of damage in a fiber bundle model in which the range of interaction of fibers varies through an adjustable stress transfer function recently introduced. We find that the lifetime of the material exhibits a crossover from mean field to short range behavior as in the static case. Numerical calculations showed that the value at which the transition takes place depends on the system's disorder. Finally, we have performed a microscopic analysis of the failure process. Our results confirm that the growth dynamics of the largest crack is radically different in the two limiting regimes of load transfer during the first stages of breaking.Comment: 8 pages, 7 figures, revtex4 styl

Fuzzy logic based de-noising of ultrasound signals from non-destructive testing

The paper reports on different methods of ultrasound signal de-noising. The reduction of noise is especially important for the evaluation of ultrasound transmission measurements in highly damping materials such as wood and glued laminated timber (glulam). In order to enable a reliable identification of characteristic signal parameters (such as time-of-flight or first amplitude) the poor signal to noise ratios (SNR) of ultrasound signals have to be improved by filtering methods. Conventional methods such as multiple signals averaging are used at the expense of huge data requirement, time consuming measurement procedures and signal processing. As an alternative approach in this paper a fuzzy logic based adaptive filter is applied for de-nosing in an attempt to use a lower number of experiments, i.e. to minimize data requirements. The results are compared to those of the conventional multiple signal averaging and of a moving average filter. Preliminary results demonstrate the feasibility of the application of the fuzzy filter and clearly illustrate its advantages as well as shortcomings over the conventional approach. The presented approach is one step towards the goal of real-time nondestructive testing (NDT) inspection of glulam beams by means of ultrasound methods

Elliptic integral solutions of spatial elastica of a thin straight rod bent under concentrated terminal forces

In this article we solve in closed form a system of nonlinear differential equations modelling the elastica in space of a thin, flexible, straight rod, loaded by a constant thrust at its free end. Common linearizations of strength of materials are of course not applicable any way, because we analyze great deformations, even if not so large to go off the linear elasticity range. By passing to cylindrical coordinates ρ, θ, z, we earn a more tractable differential system evaluating ρ as elliptic function of polar anomaly θ and also providing z through elliptic integrals of I and III kind. Deformed rod’s centerline is then completely described under both tensile or compressive load. Finally, the planar case comes out as a degeneracy, where the Bernoulli lemniscatic integral appears